1. Field of the Invention
This invention generally relates to methods and systems for determining a configuration for an optical element positioned in a collection aperture during wafer inspection. This invention may also include determining a configuration for a complimentary optical element positioned in an illumination aperture during wafer inspection.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail.
Many inspection tools have adjustable parameters for many of the optical elements of the tools. In this manner, the parameters for one or more optical elements (such as light source(s), polarizer(s), lens(es), detector(s), and the like) can be altered depending on the type of wafer being inspected and the characteristics of the defects of interest (DOIs) on the wafer. For example, different types of wafers may have dramatically different characteristics, which can cause the same toot with the same parameters to image the wafers in extremely different ways. In addition, since different types of DOIs can have dramatically different characteristics, inspection system parameters that are suitable for detection of one type of DOT may not be suitable for detection of another type of DOI. Furthermore, different types of wafers can have different noise sources, which can interfere with detection of DOIs on the wafers in different ways.
The number of adjustable parameters of wafer inspection tools, while advantageous in that the wafer inspection tools can be used for inspection of many different types of wafers and DOIs, means that a substantial number of different combinations of parameter values (otherwise referred to as “modes”) need to be (or should be) considered when setting up a wafer inspection recipe. For example, in order to ensure that the best possible mode available on an inspection system is selected for use in an inspection recipe, a significant number of the modes should be considered. Otherwise, the probability that the best possible mode has been evaluated and then subsequently chosen may be relatively tow.
Setting up inspection process recipes that are suitable for wafer inspection is, therefore, a non-trivial process that must often be repeated for each different type of wafer that will be inspected. As such, many different methods and systems for setting up wafer inspection recipes have been developed to make recipe setup easier and more efficient. However, not all wafer inspection recipe setup methods and systems can be used for all types of light and/or all types of inspection systems. For example, systems and methods that are created for setup of wafer inspection recipes that use coherent light may not necessarily be suitable for setup of wafer inspection recipes that use incoherent light. In addition, wafer inspection recipe setup for optimizing illumination with one type of light (e.g., incoherent light) may not necessarily be suitable for optimizing collection/detection with the same type of light.
Accordingly, it would be advantageous to develop methods and systems for determining a configuration for an optical element positioned in a collection aperture during wafer inspection that do not have one or more of the disadvantages described above.